Objective: This study aimed to compare the pelvic floor muscle (PFM) strength in nulliparous and primiparous women. Populations: The sample size was established considering a significance level of 5%, the test power of 80%, and the estimated error of 10%. According to these results and considering the range between percentages of answers as the casual error, each group was established with approximately 50 participants. Methods: 100 women were prospectively distributed into: Group G1 (n = 50) comprising by healthy nulliparous women; Group G2 (n = 50) with primiparous ones. Subjective evaluation of PFM strength was performed using transvaginal digital palpation (TDP). The objective evaluation of PFM strength was assessed using a portable perineometer. All parameters were performed at one moment in G1, and in G2, during the 20th and 36th weeks of pregnancy, and 45 days after the delivery. Results: In G2, 14 women were excluded due to the lost follow-up. The median of age was 23 years in G1 and 22, in G2, there was no statistical difference between the groups. In G1, BMI was in average 21.7 Kg/m2, and 25,0 Kg/m2 in G2, there was statistical difference between the groups (p= 0.0004). In G2, TDP evaluation showed a significant impairment of PFM strength at 36th week of pregnancy (p=0,0006) and 45 days after the vaginal delivery (p=0.0001) compared to nulliparous. Objective evaluations of PFM strength showed a significant decrease 45 days after vaginal delivery compared to nulliparas. Conclusion: Pregnancy and vaginal delivery may cause weakness of PFM.